Normal controls and patients with such neural disorders as Parkinson's Disease(PD), Alzheimer's disease (AD), progressive supranuclear palsy (PSP), essential tremor (ET), dementia with Parkinson's disease (D-PD), myasthenia gravis (MG), multiple system atrophy (MSA), diffuse Lewy body disease (DLBD), and Spinal Cord Injury (SCI). None will be cigarette smokers. The patients will be diagnosed accord to current consensus criteria. The healthy controls will be matched to the PD patients on such variables as sex, age, education level, and ethnicity. The Healthy Controls will be asked to answer questions regarding the disease state of their first degree family members to ensure that these first degree family members do not have a neurodegenerative diseases. Every effort will be made to include women and minority subjects.